1. Field of the Invention
This invention relates to a traction drive tool adapter, namely, a tool adapter with an epicyclic roller speed-increasing mechanism to be connected to main shafts of various machine tools and more particularly to such an adapter best suited for rotating a small diameter cutting tool at a high speed.
2. Description of the Prior Art
It is known from the prior art to provide a traction drive tool adapter consisting of a rotary portion inserted firmly into a main shaft of a machine tool, a fixed portion detachably joined to a fixed part, for example, a main shaft head and a mounting portion to which a tool is attached for example, FIG. 9 shows a tool adapter with an epicyclic roller speed-increasing mechanism, a hollow shaft 1 at the front end section of the rotary portion and a taper shank 3 at the rear end section thereof which has a grooved flange 2 at the intermediate section of the rotary portion separately formed but unitarily combined by a coaxially inserted bolt 60 at a taper surface 61.
The reasons why the rotary portion is formed in this manner reside in that the driving pins 8 for planetary rollers 7 have to be fitted firmly by axial press fitting in the mounting bores 62 provided so as to extend axially in the cylindrical circumferential wall of the hollow shaft 1.
Thus, the planetary rollers in the rotary portion, a sun roller in the tool mount portion and an annular fixed track surface of the fixed portion are in contact with each other with a predetermined level of pressing force.
In order to disassemble the tool mount portion, there is no other way than to forcibly withdraw this portion from the front end thereof against the friction occurring due to the pressing force mentioned above, and such a method is actually employed.
In order to prevent the entry of a cutting fluid from the relative rotary portion to the interior of the adapter, regularly used oil seals S are fitted between the rotary portion A and fixed portion B and between the rotary portion and tool mount portion C as shown in FIG. 9.
In the above-described prior art traction drive tool adapter, the hollow shaft 1 at the front end section of the rotary portion and the taper shank 3 at the rear end section thereof which has a grooved flange 2 at the intermediate section of the rotary portion are separately formed and unitarily combined by the coaxially inserted bolt 60 at the taper surface 61. Therefore, the connecting rigidity of the hollow shaft 1 and taper shank 3 is low, and insufficient surface contact, which would cause the vibration of the hollow shaft 1 and taper shank 3 when they are rotated, at the taper surface 61 between the hollow shaft and taper shank inevitably occurs.
Moreover, the positional accuracy of the mounting bores 62 have influence upon the contact pressure of the planetary rollers 7 against the annular fixed track surface 32 and the outer circumferential surface of the sun roller 52.
This planetary speed traction drive tool adapter has no suitable portions to be gripped for carrying out the disassembling of the tool mount portion. Therefore, if the tool mount portion is withdrawn forcibly against the friction occurring due to the above-mentioned press-contacting force, the tool adapter is damaged.
The oil seals serving as the means for preventing the entry of a cutting fluid from the relative rotary portion of a prior art traction drive tool adapter described above into the interior of the adapter have no problems in particular while the tool adapter is used at a low rotational speed but they generate much heat due to the friction of the contacting sections, so that various problems arise.